1. Field of the Invention
This invention relates generally to guyed construction techniques, and, more particularly, to techniques for anchoring guyed and additionally guyed towers.
2. Description of Related Art
Towers are widely used in many industries, including television transmission, radio communication, cell phone communication, wind turbines, and power transmission, to name a few.
Some towers, known as “guyed towers” or “additionally guyed towers,” rely on guy wires to maintain or assist in maintaining the towers in a vertical orientation. Generally speaking, these towers include a vertical main body, or “mast,” that stands on one end atop a base, which is generally concrete. Guy wires attach to the mast along its length, extend down and away from the mast, and attach securely to the ground using anchors. Most guyed towers are triangular in cross-section, and a minimum of three guy anchors are typically provided and are spaced apart by approximately 120-degrees to provide a stable base for holding the mast vertically. Often, guyed towers require three, six, or more guy anchors with multiple guy wires originating from different vertical levels of the tower attached to each guy anchor.
The term “guyed towers” describes towers whose masts have no independent means of support. They rely entirely upon guy wires to hold them upright. By contrast, the term “additionally guyed towers” describes towers that are essentially free standing, although they require guy wires to provide reinforcement and stability.
FIG. 1 shows a conventional guy anchor 100 for an erected tower. As shown in this example, four guy wires 110 originating from the tower's mast attach to an anchor head 114. The guy wires 110 are generally composed of steel or some other high tensile strength metal. A shaft 116 extends from the anchor head 114 and into the ground 124. Typically, the anchor head 114 and shaft 116, which are also generally made of steel, are provided as a single unit, with the shaft 116 permanently welded to the head 114. The distal end of the shaft 116 is typically buried in a steel-reinforced mass of concrete 118, also known as a “dead-man.” The weight of the dead-man 118 and the earth above it holds the shaft 116 securely in place, even in the presence of large forces on the tower due to wind and precipitation.
The typical guy anchor assembly 100 may also include turnbuckles 112. One turnbuckle 112 is generally provided for each guy wire 110. The role of the turnbuckles 112 is to fine-tune the tightness of each guy wire 110.
To prevent damage due to lightning strikes, the guy wires 110 are each electrically connected via a conductive cable 120 to a ground spike 122. The ground spike 122 is typically made of copper. The cable 120 and ground spike 122 form a low impedance path to ground. This arrangement is designed to conduct high current surges away from the shaft 116, thereby preventing damage to the shaft which could otherwise compromise the mechanical stability of the tower.
One drawback of the conventional guy anchor assembly 100 is that the anchor shaft 116 often corrodes over time. Over several years of use (and sometimes less time), corrosion may lead to a complete failure of the anchor shaft 116, which can result in a collapse of the tower it supports.
Guy anchor shaft corrosion typically affects the area of the shaft exposed to soil, i.e., underground but excluding the region encased within the dead-man 118. Corrosion may be galvanic or electrolytic in nature, or may be caused by other factors. In an effort to prevent corrosion, guy anchor shafts are typically galvanized.